This invention relates to tape-tensioning apparatus, and more particularly, to such apparatus for tensioning tape extending between two reels by basing the operation of one of the two reels on the operation of the other reel.
The need to regulate the tension in a magnetic tape in a tape transport is well-known, particularly when the transport forms part of a machine for recording signals on magnetic tape or playing back signals from such tape. The stretchability of magnetic tape is notorious and is particularly susceptible to changes in temperature and humidity. The mechanical stretching, even temporarily, of the tape causes misalignment of the magnetic domains forming a recorded signal on the tape. Excessive tension can also affect the physical wavelengths of signals recorded on the tape and thereby cause undesirable variations in the frequencies played back from the tape. The result is a deterioration in the quality of a played back signal.
In such applications, it is well-known to provide means for sensing the tape tension in a tape path extending between a supply reel and a capstan. A signal representing the tape tension may be used to control, in known manner, a motor driving the supply reel so as to tend to maintain the tape tension substantially constant. For this purpose it is known to provide a pivoted arm which carries a guide roller around which the tape guide extends to form a loop so that variation in the tape tension causes pivoting of the arm.
However, when a cassette containing tape is loaded in a transport, and just before or just after a threading cycle, the tension arms are held retracted and ready for cassette movement. In the retracted positions, the tension arms are not in contact with the tape and therefore are not available for providing control information regarding the tape tension. It is important in such situations, however, to maintain the tape in the cassette under tension so that during loading, threading and unloading, the tape extending between the reels in the cassette is in proper alignment relative to the transport mechanisms. Excess tape may become entangled or misfed. Further, it is important to eliminate slack in the tape so that when the tape is manipulated, the reels and other apparatus will not be operated at a rate which is likely to damage the tape when the slack is eliminated. Without the positioning of the tension arms against the tape, there has heretofore been no known mechanism for tensioning the tape while in the cassette at the time it is loaded and unloaded under controlled conditions.
A tape tensioning apparatus made according to the present invention provides slack-tape take-up and tensioning without requiring separate tape-tension sensing devices. More particularly, the invention provides for tape tensioning by coordinating the control of the two reels on which the tape is wound. Further, by slight modification of existing tape-controlling apparatus, the present invention may be incorporated into conventional tape transports, thereby providing a tape tensioning apparatus which is economical and compatible with existing systems.
The basis of the present invention resides in a tape-tensioning apparatus in which one tape reel is operated in a selected operating state, such as by holding the reel in a selected rotational position, and then controlling the operation of the other reel to take up the slack, if any, existing between the reels. Once any slack tape is taken up, counter-rotational forces are applied to both reels for applying a selected tension on the tape. In the preferred embodiment of the invention, a take-up reel is controlled by a servo to maintain the reel in a selected rotational position. When the reel is displaced from the selected position, energy is increased to urge the reel back toward the selected position. A second servo, responsive to the energization level of the first reel, operates the second reel to take up the slack in the tape between the two reels. Once the slack is taken up, a force is applied by the second reel to the first reel through the tape, thereby displacing it from the selected position. The energy applied to the second reel is then reduced in order to limit the tension on the tape to avoid damage to it. These and other features and advantages of the invention will be apparent from a consideration of the following description of a preferred embodiment of the invention with reference to the accompanying drawings.